Influence of inter- and intramolecular H-bonding on the mesomorphic and photoswitching behaviour of (E)-4-((4-(hexyloxy)phenyl)diazenyl)-N-phenyl benzamides.

B N Sunil,G Shanker,Gurumurthy Hegde,Paresh Kumar Behera,Ammathnadu S Achalkumar

doi:10.1039/d0ra03024d

Abstract

We report on the synthesis, phase behaviour and photoswitching studies of new azo linked rod-shaped molecules. These novel materials consist of three phenyl rings separated by a diazo, amide linkage with a hexyloxy tail and 2,4-substituents at either end of the phenyl ring. The mesomorphic behaviours, phase transition temperature including the enthalpies were characterized by polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The influence of inter- and intramolecular hydrogen bonding on mesomorphic and photoisomerization was studied. Photoisomerization studies carried out both in the solid and liquid phase show the quick E–Z transition with prolonged thermal back relaxation (Z–E) by using UV-Visible spectroscopy. This interesting behaviour could be attributed to the presence of the hexyloxy tail, lateral electron withdrawing group and the influence of inter- or intramolecular hydrogen bonding. Excellent bright and dark states were accomplished using one of these materials in optical storage device. Further tuning is necessary to employ them for real applications.

Highlights

Aromatic azobenzene compounds are most promising candidates for optical switching applications due to their photosensitivity.[1]
The azobenzene based benzamides were prepared by coupling the (E)-4-[4-(4-hexyloxy)phenylazo]benzoic acid with substituted aniline derivatives in the presence of 1,3-dicyclohexylcarbodiimide (DCC), 4-(N,N-dimethyl amino)pyridine (DMAP) as a coupling agent
The synthetic procedure and characterization data obtained from FT-IR, 1H NMR for nal compounds are compiled in Experimental section

Summary

Introduction

Aromatic azobenzene compounds are most promising candidates for optical switching applications due to their photosensitivity.[1]. Irradiation with the appropriate wavelength leads to reversible trans–cis isomerization.[3] This process assists in the major structural change and leads to a difference in the change of the polarity of the molecule.[4] Upon UV irradiation, which corresponds to the p–p* transition, there is a transformation from the thermodynamically most stable rod-like molecular form of trans isomer (E) into a meta-stable bent, cis isomer (Z). The azo chromophore exhibits a twoabsorption peak, high intensity p–p* absorption peak in the UV region and lower intensity n–p* absorption peak in the visible region.[5] The reverse isomerization can be induced in two ways, one is by shining the visible light (l $ 450 nm) whose

Methods

Results

Conclusion